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Setting our sights on Mercury (part 5)

On January 14, NASA’s MESSENGER spacecraft flew past Mercury. MESSENGER — short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging — made the first close-up observations of the innermost planet in 33 years. This flyby marked the first of three encounters with the planet, providing gravity assists necessary to place the probe in orbit around Mercury in March 2011.

January 17, 2008

Less than a week ago, terra incognita — Latin for “unknown territory” — aptly described more than half of Mercury. Although the Mariner 10 spacecraft flew past the planet 3 times in the mid-1970s, a quirk of its trajectory had the Sun lighting the same hemisphere during each encounter. So, scientists had seen detail on only 45 percent of the planet’s surface.

MESSENGER has suddenly and dramatically revealed approximately half of this previously unexplored terrain. Planetary scientists at Johns Hopkins University’s Applied Physics Lab released the first close-up photographs of this region earlier today. Mission controllers took the image at upper right as part of a wide-field mosaic. (See a larger version here; scientists have yet to stitch the mosaic together.)

The double-ringed crater at the photo’s upper right appears to be filled with smooth material, which may be volcanic in nature. After the crater formed, a major fault system disrupted the planet’s crust in this area. A prominent scarp (cliff) created by the faulting cuts across the image from the upper left. The scarp also disturbed a small crater near the image’s top left. Scientists plan to use images like this one to infer the history of Mercury’s surface.

MESSENGER observed Mercury with its full suite of instruments during the encounter. It skimmed within 125 miles (200 km) of the planet’s equator at 2:05 P.M. EST Sunday, traveling at 16,000 mph (26,000 km/h). All told, the spacecraft took more than 1,200 images of the planet and studied its surface, interior, magnetic field, and thin atmosphere.